The present invention is generally related to treatment of the heart, and in particular, non-invasive treatment of the heart using radiosurgical ablation.
A typical adult human heart beats at a rate of about 70 beats per minute. The rate is not constant, however, and changes during and following exercise, with fear or anxiety, or for other reasons. A heart can also pump arrhythmically for many reasons, including damage to the heart's electrical conduction system. Arrhythmias interfere with the heart's ability to pump blood, and can result in severe symptoms, including death.
Atrial fibrillation is one of the most common cardiac arrhythmias. Atrial fibrillation occurs in as many 50% of patients undergoing cardiac operations. Patients with chronic atrial fibrillation may suffer from symptomatic tachycardia or low cardiac output, have a risk of thromboembolic complications, and are at risk for death. Until just a few years ago many health care providers thought atrial fibrillation to be a “nuisance” arrhythmia with few consequences. However, medical research has uncovered some devastating complications, including stroke, congestive heart failure, and cardiomyopathy. Many conditions have been associated with atrial fibrillation, including thyroid disorders, valve disease, hypertension, sick sinus syndrome, pericarditis, lung disease, and congenital heart defects. Atrial fibrillation can occur at any age, but its prevalence tends to increase with age and effects men slightly more often than women.
During atrial fibrillation, the atria lose their organized pumping action. In normal sinus rhythm, the atria contract, the valves open, and blood fills the ventricles (the lower chambers). The ventricles then contract to complete the organized cycle of each heart beat. Atrial fibrillation has been characterized as a storm of electrical energy that travels across the atria, causing these upper chambers of the heart to quiver or fibrillate. During atrial fibrillation, the blood is not able to empty efficiently from the atria into the ventricles with each heart beat. Blood can then pool and become stagnant in the atria, creating a site for blood clot formation. Such clot formation can become a primary source of stroke in patients with atrial fibrillation.
Non-surgical treatments are sometimes effective in treating atrial fibrillation. Several drugs are known, but may have significant side effects and are not ideal for treatment of acute fibrillation. Pharmacological therapies are also associated with adverse effects in a significant proportion of patients. Moreover, although electrical cardioversion (alone or in combination with anti-arrhythmic therapy) is often effective in restoring sinus rhythm, high recurrence rates of atrial fibrillation have been reported.
A number of invasive surgical procedures have been proposed for treatment of atrial fibrillation. Invasive procedures involving direct visualization of the tissues include the Maze procedure. Dr. James Cox and others proposed the original Cox-Maze procedure in which the atria are surgically dissected and then repaired. In the Maze procedure, for example, ectopic re-entry pathways of the atria are interrupted by the scar tissue formed using a scalpel or the like. The pattern of scar tissue prevented recirculating electrical signals which can result in atrial fibrillation.
The Maze surgical procedure has been simplified by the use of cryoprobes, radio frequency (RF) probes, and laser probes to effect the pattern of scar tissue. For example, ablation is sometimes used to terminate arrhythmias by introducing a catheter into the heart and directing energy at specific areas of heart tissue. By using a transarterial catheter to deliver the energy to the atria under fluoroscopy, interventional cardiologists have treated atrial fibrillation in a less-invasive manner. RF energy has been used successfully to terminate arrhythmias by introducing the catheter into the heart and directing the RF energy at specific areas of the heart tissue. Nonetheless, there is still a need for improved non-invasive treatments of arrhythmia.